Trucking is the primary mode of long-distance and short-haul transport for goods and materials in the United States, and many other countries. Trucks typically include a motorized cab in which the driver sits and operates the vehicle. The cab is attached to a box-like cargo section. Smaller trucks typically include an integral cargo section that sits on a unified frame which extends from the front wheels to the rear wheel assembly. Larger trucks often include a detachable cab unit, with multiple driven axles, and a separate trailer with a long box-like cargo unit seated atop two or more sets of wheel assemblies. These truck assemblages are commonly referred to as “semi-trailers” or “tractor trailers.” Most modern trucks' cabs, particularly those of tractor trailers, have been fitted with aerodynamic fairings on their roof, sides and front. These fairings assist in directing air over the exposed top of the box-like cargo body, which typically extends higher (by several feet) than the average cab roof. The flat, projecting front face of a cargo body is a substantial source of drag, above the cab roof. The use of such front-mounted aerodynamic fairings in recent years has served to significantly lower drag and, therefore, raise fuel economy for trucks, especially those traveling at high speed on open highways.
However, the rear end of the truck's cargo body has remained the same throughout its history. This is mainly because most trucks include large swinging or rolling doors on their rear face. Trucks may also include a lift gate or a lip that is suited particularly to backing the truck into a loading dock area so that goods can be unloaded from the cargo body. It is well-known that the provision of appropriate aerodynamic fairings (typically consisting of an inwardly tapered set of walls) would further reduce the aerodynamic profile of the truck by reducing drag at the rear face. The reduction of drag, in turn, increases fuel economy.
To improve the aerodynamics of a truck or trailer cargo body by reducing drag, several solutions (i.e. rear-drag-reduction devices) have been provided that focus on trucks having swinging doors, which are not always readily applicable to cargo bodies having rolling doors. For useful background information on aerodynamic structures for swinging cargo doors, refer to commonly assigned U.S. patent application Ser. No. 12/122,645, entitled REAR-MOUNTED AERODYNAMIC STRUCTURE FOR TRUCK CARGO BODIES, by Smith et al., and U.S. patent application Ser. No. 12/903,770, entitled REAR-MOUNTED AERODYNAMIC STRUCTURE FOR TRUCK CARGO BODIES, by Smith et al., which are both incorporated herein by reference.
Only recently has an effort been made to improve the aerodynamic efficiency of these vehicles with the user of underbody fairings or “skirt” devices to reduce the aerodynamic drag of the trailer. However, there is currently no device that extends to cover the region behind the bogeys through to the rear plane of the trailer. This is primarily due to the fact that the position of the bogeys are frequently adjusted based on loading scenario for a given trip as well as in accordance with some state laws that mandate specific locations of the bogeys.
Still a further challenge is to improve the airflow passing under the cargo body as this space is generally configured to optimize mechanical and clearance considerations rather than aerodynamic considerations. One particular problem affecting the solutions to this is the movability of the wheel bogeys (clusters of two-three-axle wheel sets at the rear of the cargo body/trailer), thus rendering it challenging to provide a stationary skirt that covers the underbody from bogeys rearwardly to the rear of the cargo body, so as to form a continuous bottom aerodynamic envelope for the body. More particularly, it is desirable to provide a mechanism that increases the aerodynamic effectiveness of the cargo body. It is also desirable to affect the airflow, for example, in relation to a rearwardly located pocket of the cargo body provided by a rear-mounted aerodynamic structure. To this end, it is desirable to direct air away from the particular pocket created by exemplary rear aerodynamic structures such as those generated by, for example, the above-incorporated U.S. patent application Ser. Nos. 12/122,645 and 12/903,770 to Smith.
It is further desirable to provide an aerodynamic skirt structure for the underbody that is adjustable and improves aerodynamic efficiency. It is also desirable to provide a structure that maintains improved airflow underneath the trailer at the rear of the trailer, thereby reducing drag.